1. Field of the Invention
The present invention relates to a sheet feeder and sheet feeding method for plate-shaped members, in which thin plate-shaped members such as printing plates stacked on a bottom plate of a cassette, are taken out one-by-one from the uppermost layer by being sucked to a plurality of suckers.
2. Description of the Related Art
A technique has been developed, wherein a printing plate such as a photopolymer plate having a photosensitive layer (for example, a photopolymerization layer) provided on a support is used and an image is directly recorded on the photosensitive layer (photopolymerization layer) of the printing plate by a laser beam or the like (an automatic exposure apparatus for printing plates). In such a technique, an image can be rapidly recorded on the printing plate.
In the automatic exposure apparatus for printing plates, when a cassette in which a large number of printing plates in a stack are accommodated, is mounted at a predetermined position, the printing plates are taken out by a sheet feeder one-by-one from the uppermost printing plate and transferred to an exposure section.
In a cassette, the printing plates may be stacked with interleaf papers interposed therebetween so as to protect the printing surfaces of the plates. The printing plates and the interleaf papers are alternately stacked with one another, and scratching or the like of the photosensitive layer and the support for a printing plate adjacent thereto, contacting each other, is prevented. In the sheet feeder in which the printing plates stacked as described above are taken out from the cassette one-by-one, an uppermost interleaf paper is removed, and thereafter, the uppermost printing plate within the cassette is lifted up by being sucked to a plurality of suckers (suction cups) which are disposed so as to face each other along one end of the printing plate.
In the sheet feeder, it is necessary that the plurality of suckers closely contact the printing plate so that the printing plate may be reliably suction adhered to the suckers. Accordingly, adjustment of position is required in the sheet feeder so as to allow the plurality of suckers to contact the uppermost printing paper substantially at the same time.
There are cases in which the cassette is provided with separation plates which are provided such that the peripheral edge of a printing plate is caught by the separation plates when the printing plate sucked to the suckers is lifted up. The separation plates are mounted at predetermined positions in the cassette and bends the printing plate sucked to the suckers, between the separation plates and the suckers by lifting up the printing plate to a predetermined height with respect to the separation plates. As a result, an interleaf paper closely contacting the raised printing plate, or a subsequent printing plate is separated from the raised printing plate. Accordingly, only the uppermost printing plate can be taken out from the cassette.
However, in the sheet feeder as described above, positions at which a plurality of suckers are mounted, need to be precisely adjusted at the time of assembling in order that plate-shaped members such as printing plates be reliably suction adhered to the plurality of suckers. Further, it is necessary that an end of the plate-shaped member be bent between the separation plates and the suckers at an appropriate curvature so as to reliably raise only one plate-shaped member. Accordingly, it is necessary that positions to which the suckers suction adhering to the plate-shaped member are moved, be precisely adjusted with respect to the separation plates mounted in the cassette.
The above-described adjustment of position results in that assembling of the sheet feeder may be complicated. Further, when maintenance, for example, replacement of parts such as suckers is carried out, adjustment of positions thereof may be required again. As a result, maintenance becomes complicated.
The present invention has been devised in view of the above-described circumstances, and an object thereof is to achieve improvement in assembling efficiency by facilitating adjustment at the time of assembling and provide a sheet feeding method for plate-shaped members, in which plate-shaped members stacked on a bottom plate of a cassette can be reliably taken out one-by-one by a plurality of suckers.
In order to achieve the above-described object, a first aspect of the present invention is a sheet feeding method for plate-shaped members, in which the uppermost layer of plate-shaped members stacked on a bottom plate of a cassette which is disposed so as to face predetermined positions of a plurality of suction nozzles, is raised by being suction adhered to the plurality of suction nozzles and taken out from the cassette. In this method, the suction nozzles are moved from preset original positions thereof to the bottom plate of the cassette at a predetermined speed, the state in which the suction nozzles have come close to the uppermost plate-shaped member and moved to a predetermined position, is detected by an approach detecting device, and the suction nozzles are moved downward based on an amount of movement which is set so that the plurality of suction nozzles each abut against the plate-shaped member, thereby allowing the suction nozzles to suction adhere to the uppermost plate-shaped member.
According to the present invention, the suction nozzles are moved downward to positions which are previously set so that all of the suction nozzles abut against the plate-shaped member. As a result, even if the positions at which the suction nozzles are mounted, may not be located at the same height, the plate-shaped member can reliably be suction adhered to all of the suction nozzles.
Accordingly, no high accurate positioning of the suction nozzles at the time of assembling is required, and an assembling operation of the suction nozzles becomes easy.
In the present invention, preferably, the plurality of suction nozzles and the approach detecting device are integrally moved toward the bottom plate of the cassette having no plate-shaped member accommodated therein, and the state in which the suction nozzles have come close to the bottom plate of the cassette and moved to a predetermined position, is detected by the approach detecting device, a distance by which the suction nozzles move until a detected pressure of a pressure detecting device disposed between the suction nozzles and a negative pressure source reaches a predetermined value, and the distance by which the suction nozzles move, is set as the amount of movement.
According to the present invention, an amount by which the suction nozzles move until all of the suction nozzles suction adhere to the bottom plate of the cassette after the bottom plate of the cassette has been detected by the approach detecting device, is previously measured and set. That is, the position at which the plate-shaped member is reliably suction adhered to a suction nozzle which has not been mounted at the same height as others, is set.
As a result, the operation of setting the position at which the plate-shaped member is reliably suction adhered to the plurality of suction nozzles, and setting the amount by which the suction nozzles move, is automated and the setting operation can be carried out simply.
Further, according to the first aspect of the present invention, preferably, when the suction nozzles suction adhering to the plate-shaped member is moved upward to a predetermined position with respect to separation plates provided in the cassette at predetermined positions facing a peripheral edge of the plate-shaped member, so that the plate-shaped member is bent between the suction nozzles and the separation plates at a predetermined curvature, respective positions of the suction nozzles with respect to the original positions are set based on a distance by which the suction nozzles move from the original positions until the suction nozzles suction adhere to the bottom plate of the cassette.
According to the above-described structure, based on the speed at which the suction nozzles move downward, and the time in which the suction nozzles move downward, proper positions at which the plate-shaped member is separated by the suction nozzles, are set with respect to the original positions of the suction nozzles. As a result, adjustment of the original positions of the suction nozzles at the time of assembling, and adjustment of the separation positions can be simplified, and assembling efficiency of the sheet feeder by which the plate-shaped members can be reliably taken out one-by-one can be improved.
A second aspect of the present invention is a method for removing a plate-shaped member for sheet feeding from a stack of plate-shaped members supported on a bottom plate of a cassette, the method comprising the steps of: positioning suction nozzles at preset original positions relative to the bottom plate of the cassette, facing the stack; moving the suction nozzles from the preset original positions to a first position in close proximity to the stack based on information from an approach detection mechanism; moving the suction nozzles an additional amount predetermined to abut each suction nozzle against the stack; withdrawing the suction nozzles from the stack while applying reduced pressure to the suction nozzles to suction adhere a plate shaped member thereto and remove the plate-shaped member from the stack for sheet feeding.
A third aspect of the present invention is a sheet feeder for plate-shaped members, comprising: a cassette in which plate-shaped members are accommodated in a stack; a suction unit including at least one suction nozzle which is capable of suction adhering to a plate-shaped member when supplied with reduced pressure, a frame supporting the suction nozzle, and a motor which drives movement of the frame so that the suction nozzle is moved close to and apart from a plate-shaped member in the cassette, and a control system which controls operation of the motor for controlling a distance between the suction nozzle and the plate-shaped member.
As described above, the present invention has an excellent effect in that positions at which suction nozzles are mounted at the time of assembling of a sheet feeder, and original positions of the suction nozzles can be adjusted extremely easily, thereby improving assembling efficiency of the suction nozzles and facilitating maintenance thereof.